Field concentrating antennas for magnetic position sensors

ABSTRACT

A medical device is configured for diagnosis or treatment of a tissue within a body. The medical device comprises an elongate member and a position sensor. The elongate member is configured to be received within the body, and has a lumen extending between a proximal end and a distal end. The position sensor is disposed within the lumen proximate the distal end of the deformable member. The position sensor comprises a coil wound to form a central passage and configured to generate a current flow when subject to a magnetic field, and a high-permeability antenna having at least a portion disposed outside the central passage to concentrate the magnetic field into the coil and increase the current flow.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.62/133,993, 16 Mar. 2015, which is hereby incorporated by reference asthough fully set forth herein.

BACKGROUND

a. Field

The instant disclosure relates to magnetic sensors, such as those usedin medical positioning systems. In one embodiment, the instantdisclosure relates to antennas for increasing the signal strength ofmagnetic sensors.

b. Background Art

Medical positioning systems have the capability of tracking a medicaldevice within a known three-dimensional tracking space. Typical medicaldevices used with medical positioning systems include catheters,introducers, guide wires and the like. Each of these medical devices mayuse elongate, flexible shafts on which various operational elements,such as electrodes, are used to perform various diagnosis or treatmentprocedures, such as mapping and ablation, on anatomy, such as the heart.

Some types of medical positioning systems utilize a plurality ofmagnetic fields to induce voltage in a position sensor having one ormore coils in order to determine the location of that sensor within athree-dimensional space defined by the magnetic fields. The voltageinduced in such sensors can be measured by an electronic control unit asa signal indicative of the location of the sensor. The reliability andaccuracy of the magnetic positioning system is related to thedependability of the sensor signal. As such, it is beneficial toincrease the strength of the voltage induced in the coil.

One method of increasing the output strength of the sensor is toposition a high permeability core within the coil winding to increasethe electric voltage generated by the coil. The presence of the coreincreases the magnetic flux density by drawing magnetic field linestoward the sensor. Once such sensor coil and core combination isdescribed in U.S. Pat. No. 7,197,354 to Sobe, entitled “System forDetermining the Position and Orientation of a Catheter.”

The effectiveness of prior art cores is limited by the geometry of thesensor and the medical device into which it is installed. For a medicaldevice having an elongate, flexible shaft, it is desirable that thedevice have a small diameter, e.g., less than 19 French (approximately6.33 millimeters), so as to enable movement through the vasculature.Sensors used within typical medical devices can be even smaller, on theorder of 1 French (0.33 millimeters) or less. As such, the spacesavailable for the position sensor within the medical device and the corewithin the sensor are small.

The foregoing discussion is intended only to illustrate the presentfield and should not be taken as a disavowal of claim scope.

BRIEF SUMMARY

The instant disclosure relates to position sensors used in medicaldevices for use with medical positioning systems. Such medical devicesmay comprise mapping and ablation catheters for diagnosing and treatingcardiac arrhythmias via, for example, radio frequency (RF) ablation. Inparticular, the instant disclosure relates to antennas, concentrators,levers, or similar structures for inducing magnetic flux flow within aposition sensor and thereby increasing the signals generated by theposition sensor.

In one embodiment, a medical device is configured for diagnosis ortreatment of a tissue within a body. The medical device comprises anelongate, deformable member and a position sensor. The elongate memberis configured to be received within the body, and has a lumen extendingbetween a proximal end and a distal end. The position sensor is disposedwithin the lumen proximate the distal end of the deformable member. Theposition sensor comprises a coil wound to form a central passage andconfigured to generate a voltage when subject to a magnetic field, and ahigh-permeability antenna having at least a portion disposed outside thecentral passage so as to concentrate the magnetic field into the coiland increase the resulting voltage.

In another embodiment, a position sensor assembly for a medical devicecomprises a body defining an internal lumen, a wire winding supported bythe body, and a magnetic flux antenna disposed outside of the wirewinding and within the body.

In yet another embodiment, a medical device comprises an elongate sheathdefining a lumen, a position sensor disposed within the lumen, anelectrode exposed to an exterior of the elongate sheath, and a magneticantenna disposed within the sheath apart from the position sensor.

In still another embodiment, a method of increasing the signal output ofa magnetic position sensor comprises configuring a magnetic positionsensor comprising a coil to generate a voltage when subject to amagnetic field, mounting the position sensor within a medical device,and placing at least a portion of a high permeability antenna outside ofthe magnetic position sensor so as to be configured to concentrate amagnetic field into the coil and increase the current flow.

The foregoing and other aspects, features, details, utilities, andadvantages of the present disclosure will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a medical imaging system forgenerating and displaying data on a display screen using a medicaldevice having a position sensor.

FIG. 2 is a partial cross-sectional view of a distal portion of themedical device of FIG. 1 showing one embodiment of a field concentratingantenna for a magnetic position sensor in which the antenna is locatedadjacent the position sensor.

FIG. 3 is a cross-sectional view of the magnetic position sensor andfield concentrating antenna of FIG. 2 showing the presence of aconventional core within a central passage of the position sensor.

FIG. 4 is a schematic diagram of the magnetic position sensor and thefield concentrating antenna of FIG. 3 illustrating the presence ofmagnetic flux lines and induced current flow.

FIG. 5 is a partial cross-sectional view of a distal portion of amedical device showing the location of two field concentrating antennasrelative to a magnetic position sensor.

FIGS. 6A and 6B are radial and axial cross-sectional views,respectively, of a second embodiment of a field concentrating antennaand for a magnetic position sensor in which the antenna comprises anarcuate thin film extending through the position sensor.

FIGS. 7A and 7B are radial and axial cross-sectional views,respectively, of a third embodiment of a field concentrating antenna andfor a magnetic position sensor in which the antenna comprises anelongated thin film extending from the position sensor.

FIGS. 8A and 8B are radial and axial cross-sectional views,respectively, of a fourth embodiment of a field concentrating antennaand for a magnetic position sensor in which the antenna comprises aplurality of elongated strips positioned adjacent the position sensor.

FIG. 9 is a cross-sectional view of a fifth embodiment of a fieldconcentrating antenna for a magnetic position sensor in which theantenna is located remotely from the position sensor.

FIG. 10 is a schematic representation of a core with a coil winding onit similar to what is shown in FIG. 4.

FIG. 11 is a fragmentary, isometric view of the core depicted in FIG. 10(e.g., a Mu metal core).

FIG. 12 is a fragmentary, isometric view of an alternative core composedof an inner cylindrical member constructed from a polymer (e.g.,polyimide) and an outer cylindrical member constructed from a highpermeability material (e.g., Metglas).

FIG. 13 is a schematic representation of a cylindrical polymer tube(e.g., a polyimide tube) having a plurality of strips constructed fromhigh permeability material (e.g., Metglas) mounted on its exteriorsurface.

FIG. 14 is similar to FIG. 13, but schematically depicts a polymer tube(e.g., a polyimide tube) having a plurality of strips constructed fromhigh permeability material (e.g., Metglas) mounted on its interiorsurface.

FIG. 15 is similar to FIG. 13, and is a fragmentary, isometric view thatschematically depicts a Metglas ribbon or strip mounted on the exteriorsurface of a polyimide tube.

FIG. 16A schematically depicts the embodiment of FIG. 15 at a laterstage of manufacture, wherein the Metglas ribbon has been mounted to thepolyimide tube by a heat shrink casing.

FIG. 16B schematically depicts the embodiment of 16A with a wire windingwrapped around the polyimide tube and Metglas strip

FIG. 17 is a representative irrigated catheter that includes a core andwinding similar to that shown in FIG. 16B.

FIG. 18 depicts braided strips of high permeability material (e.g.,braided Metglas strips) mounted on the exterior of a polymer tube (e.g.,a polyimide tube).

FIGS. 19-22 show various sample braid patterns for the high permeabilitymaterial depicted in, for example, FIG. 18 separated from the polymertube.

FIG. 23 depicts a helical coil of high permeability material (e.g., aMetglas ribbon) wrapped on the outer surface of a polymer tube (e.g., apolyimide tube).

FIG. 24 is a cross-sectional view of an alternative, composite core fora magnetic position sensor, wherein two arcuate strips of the corecomprise high permeability material (e.g., Metglas) and wherein theadjacent arcuate strips of the core comprise a polymer material (e.g.,polyimide).

FIG. 25 is a cross-sectional view similar to what is shown in FIG. 24,but depicts a composite core comprising four arcuate strips of a highpermeability material (e.g., Metglas) mounted between four arcuatestrips of a polymer material (e.g., polyimide).

FIG. 26 depicts an enlarged, fragmentary section of a core wallcomprising a Metglas segment adjacent to a polyimide segment.

FIG. 27 is similar to FIG. 26, but depicts an embodiment wherein theadjacent Metglas and polyimide sections are encapsulated by an innerwall of polyimide and an outer wall of polyimide.

FIG. 28 depicts an embodiment similar to what is shown in FIG. 15 with apolyimide core having a Metglas strip attached to its outer surface thatalso includes an outer layer of polyimide to encapsulate the Metglas andhold it in place on the outer surface of the inner polyimide tube.

FIG. 29 depicts a possible intermediate step where a thermal plasticstrip stabilizer may be used to keep the Metglas strip in position onthe outer surface of the inner polyimide tube during construction of,for example, a composite core such as the one depicted in FIG. 27 orFIG. 28.

FIG. 30 depicts how signal strength from a magnetic position sensorconstructed according to the disclosed embodiments may vary dependingupon how the strips of, for example, Metglas are cut from a larger sheetand whether those Metglas strips are laminated or placed adjacent toeach other.

FIG. 31 schematically depicts a sheet of Metglas material and possiblecut lines (shown as dashed lines) for creating Metglas strips/ribbonsfor use in the various embodiments disclosed herein.

FIG. 32 depicts a “laminated” configuration of two Metglas strips asthat term is referenced in FIG. 30.

FIG. 33 depicts a “side” construction of Metglas strips as that term isused in FIG. 30.

FIG. 34 includes some lines representing signal strength as a functionof Metglas strip length (also taking into account two different strippositions relative to the wire coil position), and other linesrepresenting Metglas strip offset from a coil end or the coil endsversus strip length (also taking into account two different strippositions relative to the wire coil position).

DETAILED DESCRIPTION OF EMBODIMENTS

Several embodiments of field concentrating antennas for magneticposition sensors are disclosed herein. In general, these fieldconcentrating antennas are used in medical devices to increase theoutput signal of position sensors used in conjunction with medicalpositioning systems, particularly magnetic positioning systems. In oneembodiment, the antennas help produce high gain induction sensors thatcan be used within medical devices used in conjunction with magneticmedical positioning systems. Details of the various embodiments of thepresent disclosure are described below with specific reference to thefigures.

FIG. 1 is a schematic representation of medical imaging system 10 fordetermining the position of catheter 12 relative to a model of an organof patient 14, as well as for generating and displaying the model andrelated information on display unit 16. System 10 includes moving imager18, which includes intensifier 20 and emitter 22, and magneticpositioning system (MPS) 24, which includes position sensor 26 and fieldgenerators 28. Electrophysiology map information and cardiac mechanicalactivation data pertaining to the model generated by medical imagingsystem 10 is displayed on computer display 16 to facilitate diagnosisand treatment of patient 14. The present disclosure describes a way toincrease the signal output of a position sensor located within catheter12 so that system 10 is better able to process data collected bycatheter 12. For example, catheter 12 may include a coil in which avoltage is induced by the presence of a magnetic field generated by MPS24. The ability of the coil to interact with the magnetic field, andthereby generate current, is increased with the use of the fieldconcentrating antennas of the present disclosure.

Moving imager 18 is a device which acquires an image of region ofinterest 30 while patient 14 lies on operation table 32. Intensifier 20and emitter 22 are mounted on C-arm 34, which is positioned using movingmechanism 36. In one embodiment, moving imager 18 comprises afluoroscopic or X-ray type imaging system that generates atwo-dimensional (2D) image of the heart of patient 14.

MPS 24 includes a plurality of magnetic field generators 28 and catheter12, to which position sensor 26 is mounted at a distal end and handle 38is connected at a proximal end. MPS 24 determines the position of thedistal portion of catheter 12 in a magnetic coordinate system generatedby field generators 28, according to output of position sensor 26. Inone embodiment, MPS 24 comprises a MediGuide gMPS magnetic positioningsystem, as is commercially offered by St. Jude Medical, Inc., thatsimultaneously generates a three-dimensional (3D) model of the heart ofpatient 14.

C-arm 34 positions intensifier 20 above patient 14 and emitter 22underneath operation table 32. Emitter 22 generates, and intensifier 20receives, an imaging field F_(I), e.g., a radiation field, thatgenerates a 2D image of area of interest 30 on display 16. Intensifier20 and emitter 22 of moving imager 18 are connected by C-arm 34 so as tobe disposed at opposites sides of patient 14 along imaging axis A_(I),which extends vertically with reference to FIG. 1 in the describedembodiment. Moving mechanism 36 rotates C-arm 34 about rotation axisA_(R), which extends horizontally with reference to FIG. 1 in thedescribed embodiment. Moving mechanism 36 or an additional movingmechanism may be used to move C-arm 34 into other orientations. Forexample, C-arm 34 can be rotated about an axis (not shown) extendinginto the plane of FIG. 1 such that imaging axis A_(I) is rotatable inthe plane of FIG. 1. As such, moving imager 18 is associated with 3Doptical coordinate system having x-axis X_(I), y-axis Y_(I), and z-axisZ_(I).

MPS 24 is positioned to allow catheter 12 and field generators 28 tointeract with system 10 through the use of appropriate wired and/orwireless technology. Catheter 12 is inserted into the vasculature ofpatient 14 such that position sensor 26 is located at area of interest30. Field generators 28 are mounted to intensifier 20 so as to becapable of generating magnetic field F_(M) in area of interest 30coextensive with imaging field F_(I). MPS 24 is able to detect thepresence of position sensor 26 within the magnetic field F_(M). In oneembodiment, position sensor 26 may include three mutually orthogonalcoils, as described in U.S. Pat. No. 6,233,476 to Strommer et al., theentire content of which is incorporated herein by reference in itsentirety for all purposes. As such, MPS 24 is associated with a 3Dmagnetic coordinate system having x-axis X_(P), y-axis Y_(P), and z-axisZ_(P).

The 3D optical coordinate system and the 3D magnetic coordinate systemare independent of each other, that is they have different scales,origins, and orientations. Movement of C-arm 34 via moving mechanism 36allows imaging field F_(I) and magnetic field F_(M) to move relative toarea of interest 30 within their respective coordinate system. However,field generators 28 are located on intensifier 20 so as to register thecoordinate systems associated with moving imager 18 and MPS 24. Thus,images generated within each coordinate system can be merged into asingle image shown on display unit 16. Moving imager 18 and MPS 24 mayfunction together as is described in United States Pub. No. US2008/0183071 to Strommer et al., the entire content of which isincorporated herein by reference in its entirety for all purposes.

Display unit 16 is coupled with intensifier 20. Emitter 22 transmitsradiation that passes through patient 14. The radiation is detected byintensifier 20 as a representation of the anatomy of area of interest30. An image representing area of interest 30 is generated on displayunit 16, including an image of catheter 12. C-arm 34 can be moved toobtain multiple 2D images of area of interest 30, each of which can beshown as a 2D image on display unit 16.

Display unit 16 is coupled to MPS 24. Field generators 28 transmitmagnetic fields that are mutually orthogonal, corresponding to axes ofthe 3D magnetic coordinate system. Position sensor 26 detects themagnetic fields generated by field generators 28. The detected signalsare related to the position and orientation of the distal end ofcatheter 12 by, for example, the Biot Savart law, known in the art.Thus, the precise position and location of the distal end of catheter 12is obtained by MPS 24 and can be shown in conjunction with the 2D imagesof area of interest 30 at display unit 16. Furthermore, data fromposition sensor 26 can be used to generate a 3D model of area ofinterest 30, as is described in U.S. Pat. No. 7,386,339 to Strommer etal., the entire content of which is incorporated herein by reference inits entirety for all purposes.

The voltage output of position sensor 26 is increased by placement of ahigh magnetic permeable material adjacent to, in close proximity to,underneath, next to, or otherwise disposed in relation to the coilwindings forming the sensor to increase magnetic field interaction withthe position sensor. Increased voltage output of the position sensorincreases the signal generated by the position sensor that isinterpreted by MPS 24 and system 10. Improved signal strength canimprove the accuracy of the placement of catheter 12 (i.e., positionsensor 26) relative to the anatomy generated by emitter 22 andintensifier 20 on display screen 16, such as by increasing thesignal-to-noise ratio of MPS 24. Furthermore, hardware used withinsystem 10 may be able to use larger amplification levels and magnetictransmission frequencies. This is beneficial as it lowers theenvironmental influence to magnetic transmitters, which drives downpositional error. Improved signal strength also permits smaller formfactors for the design of the sensor, while maintaining the same signaloutput.

FIG. 2 is a partial cross-sectional view of the distal portion ofablation catheter 12 of FIG. 1 showing position sensor 26 and fieldconcentrating antenna 40. Catheter 12 also includes sheath 42, flexibletip 44, tip cap 46, electrodes 48A, 48B and 48C, fluid tube 50, flexcircuit 52, plug 54, spring coil 56, and thermocouple 58.

Tube 50 is disposed concentrically within sheath 42 and is attachedtherein by an adhesive or the like. Tube 50 may be a PEEK tube or it maybe made of other suitable nonconductive materials. Plug 54 is positionedaround tube 50 to maintain tube 50 centered within sheath 42 and tofacilitate joining of flexible tip 44 to sheath 42. For example,flexible tip 44 may be metallurgically joined to plug 54 at a flange.Flexible tip 44 includes incisions that allow flexible tip 44 to bend.Spring coil 56 is supported between tip cap 46 and plug 54 surroundingtube 50 and provides structural integrity to sheath 42 and resilientlymaintains flexible tip 44 in a predetermined configuration when at restand no force is placed on flexible tip 44. In the embodiment shown, thepredetermined rest configuration orients the longitudinal axis offlexible tip 44 to follow a straight line coincident with a central axisof catheter 12.

Band electrodes 48A and 48B are provided on sheath 42 and may be usedfor diagnostic purposes or the like. Band electrode 48C is provided onsheath 42 and may be used for ablating tissue. Conductor wires 60A, 60Band 60C are provided to connect electrodes 48A, 48B and 48C,respectively, to the proximal portion of catheter 12, such as handle 38,for ultimate connection with MPS 24 and system 10. Thermocouple 58 isdisposed in tip cap 46 and may be supported by an adhesive. Conductorwire 61 connects thermocouple 58 to the proximal portion of catheter 12,such as handle 38.

Position sensor 26 circumscribes tube 50 within sheath 42. Positionsensor 26 is coupled to flex circuit 52, which includes conductor 62 toconnect to the proximal portion of catheter 12, such as handle 38. Inone embodiment, position sensor 26 comprises a wound conductor coil thatis receptive to magnetic fields. Antenna 40 is positioned in closeproximity to position sensor 26 in order to facilitate a higher amountof magnetic flux interacting with position sensor 26 (as opposed toconfigurations without antenna 40).

In operation, catheter 12 is inserted into the vasculature of a patientsuch that flexible tip 44 is located at an area where it is desirable toperform a medical procedure (e.g., near tissue that is to be ablated).Ablation energy (e.g., RF energy) could then be delivered through tipcap 46, flexible tip 44, and/or one or more of band electrodes 48A, 48B,and 48C. Flexible tip 44 is able to bend so as to allow, for example,band electrode 48C to contact the tissue with a reduced risk ofpuncturing or otherwise damaging the tissue. As mentioned, bandelectrodes 48A, 48B, and 48C may be used to gather physiological datafrom the patient.

Tube 50 allows an irrigation fluid to be conveyed to the ablation sitein order to control the temperature of the tissue and remove impuritiesfrom the site. For example, irrigation fluid from an external storagetank may be connected to handle 38 whereby the fluid is introduced, e.g.pumped, into tube 50. Tube 50 is provided with (or is affixed to adistal component that is provided with) radial ports 64 to allow fluidto escape tube 50. Fluid is permitted to escape catheter 12 at tip ports66 in tip cap 46 and ports 68 in flexible tip 44 formed by the notedincisions. Thermocouple 58 permits operators of system 10 to monitor thetemperature of or near the ablation site.

Position sensor 26 allows for accurate placement of, for example, bandelectrode 48C within the patient. Antenna 40 increases the signalgenerated by position sensor 26 to increase the accuracy of the locationdata. As discussed below, antenna 40 comprises a mass of highpermeability material that is placed in close proximity to positionsensor 26 to funnel or concentrate magnetic flux into position sensor 26to increase the current generated within the coil winding of positionsensor 26. Additional details of the construction of sheath 42, flexibletip 44, fluid tube 50, spring coil 56, and other components of catheter12 can be found in, for example, United States Pub. No. US 2010/0152731,now U.S. Pat. No. 8,979,837, and United States Pub. No. US 2011/0313417,both to de la Rama et al., the entire contents of which are incorporatedherein by reference in their entirety for all purposes. Additionaldetails of the construction of position sensor 26, flex circuit 52, andother components can be found in United States Pub. No. US 2014/0200556to Sela et al., the entire content of which is incorporated herein byreference in its entirety for all purposes.

FIG. 3 is a cross-sectional view of magnetic position sensor 26 andfield concentrating antenna 40 of FIG. 2. FIG. 3 schematically depictsfluid tube 50 disposed concentrically along the axis of center line CL,with position sensor 26 and antenna 40 positioned to circumscribe tube50. Although, as shown in the other Figures, sensor 26 and antenna 40need not be axially aligned with center line C_(L). In the embodimentshown, position sensor 26 comprises a coil winding (see coil windings 74of FIG. 4) having an internal, central passage in which core 70 isdisposed and through which tube 50 extends. The coil windings 74 ofposition sensor 26 may be formed from a length of conductive wire, suchas copper, spirally wound about center line C_(L). In one embodiment,the ends of the wire (see wires 76A, 76B of FIG. 4) extend toward theproximal portion of catheter 12 to join to flexible circuit 52 (FIG. 2).In addition to the wire routing depicted in FIG. 4, the wiring ofposition sensor 26 may extend from different locations on positionsensor 26 and may be routed to extend to other locations of catheter 12.The coil windings may be supported by a bobbin or other supportstructure (see, e.g., structure 72 of FIG. 4). In other embodiments, thecoil winding may be embedded within sheath 42.

Continuing to refer to FIG. 3, in the depicted embodiment, positionsensor 26 includes core 70, which can be used to increase the magneticflux passing through the coil windings of position sensor 26. Core 70comprises a conventional annular core constructed of high permeabilitymaterial, such as those described in the aforementioned U.S. Pat. No.7,197,354 to Sobe, the entire content of which is incorporated herein byreference in its entirety for all purposes. In the depicted embodiment,core 70 does not extend beyond the outer axial limits of position sensor26, which may be useful in winding of the wires around core 70 duringmanufacturing. In other embodiments, core 70 may extend beyond the outeraxial limits of position sensor 26. As such, the inner diameter of thecoil windings 74 comprising part of position sensor 26 needs to besufficiently large to accommodate the use of core 70. However, in otherembodiments, core 70 may have a larger diameter than position sensor 26.In yet other embodiments, position sensor 26 does not include core 70.

Antenna 40 comprises an annular body having an internal, central passagethrough which tube 50 extends. Antenna 40 is positioned adjacentposition sensor 26 and may be either in contact with position sensor 26or spaced from position sensor 26 a short distance (e.g., the width ofposition sensor 26) without the use of a remote tether (see, forexample, conductor 102 in FIG. 9). Antenna 40 is configured to generatemagnetic flux lines that pass through position sensor 26 when subject toa magnetic field, thereby bringing a larger amount of the magnetic fieldinto contact with position sensor 26 than would otherwise contactposition sensor 26 without the presence of antenna 40.

FIG. 4 is a schematic diagram of magnetic position sensor 26 and fieldconcentrating antenna 40 of FIG. 3 illustrating the presence of magneticflux lines MF₁ and MF₂, and induced current flow CF. Position sensor 26may include structure 72, such as core 70 or a bobbin, around which coilwindings 74 are wound in a spiral fashion between lead wires 76A and76B. Lead wires 76A and 76B extend from coil windings 74 to join to flexcircuit 52 (FIG. 2). As a result of being placed in a magnetic field,such as magnetic field F_(M) of FIG. 1, magnetic flux lines MF₁ areformed by coil windings 74, which induces current flow CF in coilwindings 74. The voltage V induced in coil windings 74 between leadwires 76A and 76B is defined in Equation (1) below, where =magneticpermeability (core material), N=total number of turns, A=cross-sectionalarea of core (L=length of core), and B=magnetic field strength (outputof drive coil, in P-P or RMS).

V=2πμNABf  Equation (1)

As can be seen from Equation (1), the induced voltage V is increased ifthe magnetic permeability μ increases or if the area A increases. It is,however, undesirable to increase the area A of the core due to spacelimitations within catheter 12, as well as the overall outer diametersize limitations of catheter 12. It is also not always possible tosimply increase the number of turns N of the coil without undulyaffecting the flexibility of the catheter. For example, adding windingsin the axial length makes the sensor longer, while adding winding in theradial direction makes the sensor thicker, both of which may make thecatheter undesirably stiffer.

As a result of being subject to the same magnetic field that positionsensor 26 is subject to, magnetic flux lines MF₂ are formed by antenna40. Some of magnetic flux lines MF₂ pass through position sensor 26.With reference to Equation (1), antenna 40 can be viewed as eitherincreasing the permeability μ of the core, or as increasing the magneticfield strength B impacting the core. As a result of the presence ofantenna 40, various design parameters of position sensor 26, such asvoltage V or area A, can be changed. For example, the size (e.g.,diameter D, wherein

$A = {\pi \left( \frac{D}{2} \right)}^{2}$

of coil windings 74 could be reduced without reducing the signalstrength or V by using an appropriately sized antenna 40. Additionally,antenna 40 may also permit the windings of position sensor 26 to befabricated from cheaper materials or based on connection methods to flexcircuit 52 (visible in FIG. 2), for example, while allowing for thespecific configuration of antenna 40 to generate the desired signalstrength. Also, antenna 40 can merely be configured as a mass of highpermeability material that is used to simply increase voltage V, whichincreases the signal of position sensor 26 received at MPS 24 (shown inFIG. 1). Voltage V could be further increased by including multipleantennas within catheter 12.

FIG. 5 is a partial cross-sectional view of a distal portion of ablationcatheter 12′ showing the location of field concentrating antenna 77 andfield concentrating antenna 78 relative to magnetic position sensor 26.In the depicted embodiment, antenna 78 is disposed adjacent positionsensor 26 axially opposite antenna 77. In other embodiments, antennas 77and 78 can be positioned on the same side of position sensor 26.Antennas 77 and 78 can be in contact with, adjacent to, or spaced fromposition sensor 26. Antennas 77 and 78 can be configured similarly asantenna 40 as is described with reference to FIGS. 2-4. For example,antennas 77 and 78 may each simply comprise a cylindrical bodypositioned in close proximity to coil windings 74 (visible in FIG. 4).However, in the depicted embodiment of FIG. 5, antennas 40 and 78 haveouter diameters larger than that of position sensor 26 therebydistinguishing from conventional cores that must be smaller forplacement within the position sensor. The cylindrical shape allows forother components of catheter 12′, such as tube 50, flex circuit 52(visible in FIG. 2) or lead wires, to pass therethrough.

The antennas described herein can be made of any material, withmaterials of higher magnetic permeability being more suitable. Magneticfield lines preferentially travel through materials with highpermeability. In various embodiments, Mu metals, amorphous metal alloys(also known as metallic glass alloys), or 99.95% pure iron may be used.One particular branch of Mu metals and Metglas® amorphous alloys(METGLAS is a registered trademark of Metglas, Inc. of Conway, S.C.) areboth particularly well suited for use with antennas of the presentdisclosure. As used herein, the term “Metglas” means thin amorphousmetal alloys (also known as metallic glass alloys) produced using arapid solidification process (e.g., cooling at about one million degreesFahrenheit per second), whether or not bearing the METGLAS trademark andwhether or not produced by Metglas, Inc. or one of its related entities.That said, Metglas alloy 2714A has been found to work well in certainapplications/constructions. The Metglas components used in the antennasdisclosed herein are thin ribbons/sheets of various widths that aregenerally 15-75 microns (i.e., 0.015-0.075 mm) thick, but thinner orthicker ribbons/sheets could be used. The Metglas strips discussedherein may be, for example, anywhere from approximately 0.020″ to 0.100″wide. Further, as compared to air with a magnetic permeability equal toone (i.e., μ=1), it has been found that Mu metals have a relativemagnetic permeability of approximately 50,000, 99.95% pure iron has arelative magnetic permeability of approximately 200,000, and Metglas hasa relative magnetic permeability of approximately 1,000,000.

“Magnetic permeability” as used herein, unless indicated to thecontrary, refers to the ability of a material or element to support theformation of a magnetic field within itself. It is the degree ofmagnetization that a material obtains in response to an applied magneticfield. A material with a “high magnetic permeability” as used herein,unless indicated to the contrary, means any material having a relativemagnetic permeability above the relative magnetic permeability ofMartensitic stainless steel.

The specific shape of antennas 40, 77, and 78 can be varied to achievedesirable design requirements. For round antenna shapes having adiameter D and a length L, experiments have shown that the shape of highpermeability antennas is optimized when the D/L ratio is small. Antennashaving such shape are typically long and skinny.

FIGS. 6A and 6B are radial and axial cross-sectional views,respectively, of field concentrating antenna 80 and magnetic positionsensor 82. Position sensor 82 is similar to position sensor 26 discussedwith reference to FIGS. 2 and 3, but without a core. Antenna 80comprises an arcuate thin film, sheet, or ribbon extending axiallythrough position sensor 82. As compared to a conventional sensor core,mass of antenna 80 is displaced from the interior of position sensor 82and located outside of the boundaries of position sensor 82. Clearingantenna 80 from interior portions of position sensor 82 allows forposition sensor 82 to be smaller without sacrificing signal strength, orfor placement of other components within the sensor, which increase thedesign flexibility of the medical device.

In one embodiment, antenna 80 is thin in that the radial thickness ofantenna 80 is orders of magnitude smaller that the circumferential widthor axial length of antenna 80. For example, the radial thickness ofantenna 80 may be approximately fifteen microns (i.e., 15 μm, which is0.015 mm) or less. In the depicted embodiment, the axial length ofantenna 80 is longer than the axial length of position sensor 82 so thatantenna 80 necessarily extends from position sensor 82 when arranges asshown in FIGS. 6A and 6B. However, in other embodiments, antenna 80 maybe equally long or shorter than position sensor 82, but positioned so asto extend axially out from position sensor 82 (e.g., see theconfiguration shown in FIGS. 7A and 7B, where the antenna 84 is the samelength as the magnetic position sensor 86). In the embodiment shown inFIGS. 6A and 6B, antenna 80 comprises half of a hollow cylindrical shell(i.e., is a semi-cylindrical shell or a half cylinder), although othersub-cylindrical (i.e., having less than a full circular cross section)or arcuate shapes may be used. Also, the antenna may be flat (i.e., havea square or rectangular cross section rather than an arcuate crosssection), as shown in FIGS. 7A and 7B.

FIGS. 7A and 7B are radial and axial cross-sectional views,respectively, of field concentrating antenna 84 and magnetic positionsensor 86. Antenna 84 comprises a flat thin film extending axially fromposition sensor 86. Antenna 84 is similar to that of antenna 80 of FIGS.6A and 6B, but antenna 84 is flat and axially equal in length toposition sensor 86. Antenna 84 is positioned partially within andpartially outside of position sensor 86. Antenna 84 may also be placedcompletely outside of position sensor either distally or proximally ofposition sensor 86. Antenna 84 depicts another embodiment of a fieldconcentrating antenna of the present disclosure in which the antenna canbe displaced at least partially from the interior of the position sensor86 (e.g., at least a portion of the antenna 84 extending from theinterior of the sensor 86) in order to increase design options for theoverall diameter of position sensor 86 or the contents of the interiorof position sensor 86. In other embodiments, a thin film antenna may beconfigured to extend along a majority of the length of the elongate,flexible member used in the medical device, including along any distalloop regions.

FIGS. 8A and 8B are radial and axial cross-sectional views,respectively, of a field concentrating antenna 88 and a magneticposition sensor 90. In the depicted embodiment, antenna 88 comprises aplurality of elongated strips 92A-92C positioned adjacent to positionsensor 90. As discussed above, it is desirable for field concentratingantennas of the present disclosure to have long, skinny shapes such thatthey have a small D/L ratio. Although elongated strips 92A-92C are notround, they are thin relative to their axial length. The specificcross-sectional shape of strips 92A-92C can be different in variousembodiments, and can have different thicknesses. For example, strips92A-92C may comprise segments of thin films, sheets, or ribbons.Elongated strips 92A-92C are shown being disposed in a triangularpattern at twelve o'clock, nine o'clock, and six o'clock positions withrespect to FIG. 8B. However, elongated strips 92A-92C may be positionedanywhere adjacent position sensor 90 so as to have a positive effect onthe magnetic field interface with position sensor 90 as describedherein. Elongate strips 92A-92C, and any of the magnetic field enhancingantennas described herein, may be held in place within the medicaldevice using any suitable means, such as adhesive.

In the embodiment of FIGS. 8A and 8B, a plurality of smallthickness-to-length ratio antennas are provided outside of the interiorof position sensor 90. As such, the effect of a plurality of small massantennas can have a cumulative effect in increasing the interface of theposition sensor 90 with a magnetic field. Elongated strips 92A-92Cfurther improve the design options for position sensor 90 by allowingfield concentrating antennas to be located within any available spacewithin the medical device that is in close proximity to the positionsensor. Thus, other components, such as irrigation tubes, lead wires,guide wires, etc. can be positioned without interference from a core,and the field concentrating antennas can be fitted in space where it isavailable.

In yet another embodiment, the location of position sensor 26 could bemoved away from the location for which it is configured to providelocation data by remotely tethering antenna 40 to position sensor 26, asshown in FIG. 9.

FIG. 9 is a cross-sectional view of field concentrating antenna 94 formagnetic position sensor 96 in which antenna 94 is located remotely fromposition sensor 96 within sheath 98 of catheter 100. In the embodimentof FIG. 9, field concentrating antenna 94 is remotely tethered toposition sensor 96 via conductor 102. Position sensor 96 and conductor102 are disposed within shield 104. Position sensor 96 is grounded viawire 106, which passes through opening 108 in shield 104. Sheath 98 andcatheter 100 are similar to sheath 42 and catheter 12 of FIG. 2.Likewise, position sensor 96 may be constructed similarly to positionsensor 26, or any conventional magnetic position sensor.

Antenna 94 is positioned within catheter 100 at a location where it isdesirable to accurately know the location. As depicted antenna 94 ispositioned close to tip 110, but may be positioned close to otherelements, such as diagnostic electrodes, ablation electrodes, or anyother operational element. Conventionally, a position sensor providesfeedback based on where it interacts with the magnetic field in which itis placed. Thus, it is conventionally desirable to locate the positionsensor close to the operational element for which it is desirable toknow the exact location. For example, it is desirable to know the exactlocation of the operational element on display screen 16 (shown inFIG. 1) relative to a model or image of the anatomy where the procedureis to be performed.

In the embodiment of FIG. 9, position sensor 96 can be placed withinsheath 98 at any location where space is available without regard to thespecific location within catheter 100. Antenna 94 is placed where it isdesirable to know the location in the medical positioning system.Antenna 94 interacts with the magnetic field at that location, therebygenerating a pseudo position signal that is relayed to position sensor96 by conductor 102 for generation of an actual signal that can bepassed to system 10 (shown in FIG. 1). Conductor 102 may be fabricatedfrom any suitable high permeability material, such as a Metglas ornearly pure iron. Shield 104 functions to reduce magnetic noise inposition sensor 96, and thus may be fabricated from a high permeabilitymaterial to draw magnetic field lines away from direct engagement withposition sensor 96. Shield 104 may have a variety of shapes. In thedepicted embodiment, shield 104 includes sensor portion 104A that isshaped similarly to position sensor 96, and conductor portion 104B thatis shaped similarly to conductor 102. Thus, shield 104 is positionedclosely to the elements to be shielded to minimize consumption of spacewithin catheter 100. However, shield 104 may have a simpler, cylindricaldesign to facilitate easier fabrication, but that occupies more space.As noted, shield 104 is also provided with ground wire 106.Alternatively, ground 106 may be omitted and opening 108 may beprovided. Ground 106 and opening 108 may be provide to allow outsidecommunication with position sensor 96, among other reasons.

FIG. 10 schematically depicts a typical core (e.g., a Mu metal core) ofa position sensor 112 with wire windings 114 around the core of aposition sensor. In this figure, the wire windings 114 are representedschematically and, in reality, they would likely be densely packed onthe core of the position sensor 112.

FIG. 11 is a fragmentary, isometric view of the core of the positionsensor 112 of FIG. 10 removed from the wire windings 114. In order toenhance the signal output from the magnetic position sensor, the core112 may be constructed from a high permeability material. In thisparticular figure, the core of the position sensor 112 is represented asbeing constructed from Mu metal having a thickness 116 of 0.003″. Coresof this sample thickness may, however, create space issues in moderncatheters because of the number of components contained within thecatheter body (see, for example, FIGS. 2 and 5).

FIG. 12 is a fragmentary, isometric view of an alternative core 118 fora magnetic position sensor according to the present disclosure. Thiscore 118 comprises a cylindrical polymer tube 120 (for example, a0.0002″ thick polyimide tube) surrounded by a cylinder 122 constructedfrom Metglas. Since the Metglas sheet that would be shaped into theMetglas cylinder 122 depicted in FIG. 12 may be extremely thin, forexample, 15-75 microns thick (i.e., approximately 0.00059″-0.00295″thick), the resulting core 118 would save valuable real estate insidethe catheter, freeing up space for other components. Although not shownin the figures, the Metglas on the outside of the polyimide tube mayalso have a C-shaped cross-section rather than being a complete annularshape. This configuration having a C-shaped cross section may beadvantageous over a full cylindrical configuration since it may allowmore flex lines to actually go through the center of the core than wouldgo through the center of the core if it were a complete cylinder.

FIG. 13 schematically represents an alternative configuration whereMetglas ribbons 124 are attached to the outer surface of a polymer innertube—for example a polyimide tube. In other embodiments, the ribbons 124could also be strips or wires. Although these Metglas ribbons 124 appearto be rectangularly-shaped in this figure, they each may also have acylindrical cross section.

FIG. 14 is similar to FIG. 13, but schematically depicts Metglas ribbons128 or strips or wires mounted to an inner surface of the polymer tube130 (for example, a polyimide tube).

Referring next to FIGS. 15-17, an alternative construction for amagnetic position sensor according to the present disclosure isdescribed next. FIG. 15 schematically depicts a fragmentary, isometricview of a polyimide tube 132 and a Metglas ribbon 134 attached to anouter surface of the polyimide tube 132. The Metglas ribbon could be,for example, glued in placed or wrapped with heat shrink material tohold the strip in place on the outer surface of the polyimide tube.

Referring again to FIG. 15, a plurality of high permeability ribbons orstrips could be added around the entire outer perimeter of the polymertube depicted in FIGS. 15 and 16. For example, these Metglasribbons/strips could create a single ‘picket fence’ configurationsurrounding the entire exterior of the polyimide tube. The plurality ofMetglas strips placed adjacent to each other, potentially with theirlongitudinal edges in contact, could magnetically mimic the cylindricalMetglas configurations depicted in, for example, FIG. 12.

FIGS. 16A and 16B includes two embodiments similar to what is shown inFIG. 15. In FIG. 16A, a strip 136 of high permeability material (forexample, a Metglas strip) is shown arranged longitudinally on an outersurface of a polymer tube 138 (for example, a polyimide tube). In thisparticular embodiment, a heat shrink casing 140 or sleeve holds theMetglas strip 136 on the outer surface of the polyimide tube 138. Asschematically represented in FIG. 16B, a wire 142 would be wound aroundthe outside of the assembled tube and strip assembly of FIG. 16A tocomplete the construction of the magnetic position sensor.

FIG. 17 schematically depicts a configuration of an irrigated catheter12″ employing the magnetic position sensor described above in connectionwith FIGS. 15 and 16. As shown in this figure, the magnetic positionsensor 144 is mounted around fiber optic lines 146 and a fluid lumen 148that are arranged to deliver signals and fluid, respectively, to thedistal end of the catheter 12″.

FIGS. 18-22 depict various embodiments of braided high permeabilitymaterial (for example, braided Metglas strips). These different braidconfigurations could be used as an alternative to, or in combinationwith, the longitudinally-extending strips of high permeability materialdepicted in, for example, FIGS. and 16. Also, the braid could extendalong portions of the catheter shaft (or along the entire cathetershaft) to magnetically shield the internal components of the catheter.

Referring to most particularly to FIG. 20, a plurality of loosely-woundstrips of high permeability material (for example, Metglas strips orribbons) are shown. The density of these strips (weave density) isadjustable depending upon parameters such as the flexibility of thematerial comprising the strips and the desired signal boosting function.

FIG. 23 is a fragmentary, schematic representation of an alternativeconfiguration wherein a polymer tube 150 (for example, a polyimide tube)has a helical coil 152 of high permeability material (for example,Metglas) wound around its exterior surface. Similar to what wasdescribed above in connection with FIG. 20, the pitch of this helicalcoil could be adjusted depending upon the characteristics of the highpermeability material comprising the coil and the desired signalboosting impact of the resulting magnetic position sensor. Also,although FIG. 23 shows the helical coil encircling the polymer tubemultiple times, it is possible that, in some embodiments, the helicalcoil may not fully loop around or encircle the tube even one time.

In another manufacturing option, rather than adding high permeabilitymaterial to an exterior or interior surface of a polymer tube, the highpermeability material could comprise part of a composite core,including, possibly, an extruded composite core. For example, FIG. 24depicts a composite core 154 wherein arcuate Metglas strips 156 arepresent at the 12 o'clock position and at the 6 o'clock position in thecircular cross section of this magnetic position sensor core. Those twoMetglas strips 156 are separated by arcuate sections of polymer material(for example, polyimide material). Thus, in this configuration, arcuatestrips of Metglas are positioned adjacent to arcuate sections ofpolyimide to create a core around which wire would be wound to form amagnetic position sensor. The high permeability material (Metglas in theembodiment depicted) is directly integrated into the sidewall of thecore 154 during the tube-formation process. As depicted in FIG. 24, thiscould result in, for example, the core 154 having a sidewall thicknessof approximately 0.001″, if desired.

FIG. 25 is similar to FIG. 24, but depicts a configuration having fourarcuate strips 158 of Metglas extending between four adjacent arcuatestrips of polyimide. In particular, in this configuration there is aMetglas strip shown at the 12 o'clock position, the 3 o'clock position,the 6 o'clock, and the 9 o'clock position.

FIGS. 26-29 are fragmentary views of a section of core sidewall. Forexample, FIG. 26 is a fragmentary view of a section of sidewall 160represented by the embodiments depicted in FIGS. 24 and 25. As shown inFIG. 26, the arcuate Metglas strips 162 are placed adjacent to (and areabutting in this particular configuration) polyimide strips 164. Thisagain may permit the construction of a core having a wall thickness 166of, for example, approximately 0.001″. FIG. 27 depicts an alternativecore wall construction. In this construction, a polyimide tube 168having a thickness 170 of approximately 0.0002″ comprises a cylindricalinner member. Arcuate Metglas strips 172 and arcuate polyimide strips174 similar to those shown in FIGS. 24 and 25 are then mounted on anouter surface of the inner polyimide tube. Finally, an outer polyimidetube 176 is mounted over the Metglas strips 172 and polyimide strips 174mounted on the outer surface of the inner polyimide tube 168. Thisresults in a sandwiched construction, wherein the arcuate Metglas strips172 are abutting arcuate polyimide strips 174 and all strips aresandwiched between the inner polyimide tube 168 and the outer polyimidetube 176. If the polyimide tubes are, for example, approximately 0.0002″thick and the arcuate Metglas strips 172 and the arcuate polyimidestrips 174 are held to a thickness of approximately 0.0006″, then theresulting core for the magnetic position sensor again may have asidewall thickness 178 of approximately 0.001″.

FIG. 28 depicts another alternative construction for the core for themagnetic position sensor. This configuration starts with a cylindricalpolyimide inner member 180, represented in FIG. 8 as having a wallthickness of approximately 0.0002″. A Metglas strip 182 having, forexample, a thickness 184 of 0.0006″ is then mounted to the outer surfaceof the inner polymer tube, similar to what is shown in, for example,FIG. 15. Next, a polyimide layer 186 with a thickness 188 of, forexample, approximately 0.0008″ is then overlaid on the outer surface ofthe inner polyimide tube 180 and Metglas strip 182 (or strips) as shown.This results in a core for the magnetic position sensor having sectionsthat are approximately 0.001″ thick and sections with a wall thicknessof approximately 0.0016″. The coil windings would be then wound on theouter surface of this assembly as shown in, for example, FIGS. 4, 10,and 16.

FIG. 29 depicts a potential intermediate step during the construction ofa core for a magnetic position sensor. In this embodiment, a Metglasstrip 190 is again added to (e.g., adhered to) an outer surface of acylindrical polyimide tube 192. In this embodiment, however, a thinthermal plastic strip stabilizer 194 has been placed over the Metglasstrip 190 to stabilize the strip 190 on the outer surface of thepolyimide tube 192. This thermal plastic strip stabilizer 194 may remainin place during the remaining construction of the core for the magneticposition sensor. In particular, another layer (e.g., of polyamide) couldbe added over the thermal plastic strip, similar to the outer polyimidelayer depicted in FIG. 28, or, alternatively, the coil wire could bewound directly on the outer surface of the polyimide tube with theMetglas ribbons held in place by the thermal plastic strip stabilizer.

FIG. 30 depicts the results of an experiment to measure signal strengthoutput by a magnetic position sensor while varying various parameters.In this experiment, strips of Metglas were placed in a open “universal”coil (i.e., a coil without a core) so that different cores could beplaced inside the coil while measuring the resulting voltage. WhileMetglas is an amorphous alloy, there is a preferred orientation of thematerial in relation to the orientation of the magnetic flux. This isrepresented schematically in FIG. 31, which depicts a sheet 196 ofMetglas material having a preferred orientation relative to theorientation of magnetic flux. As represented by the dash lines 198 inFIG. 31, for some of the experiments represented by lines on the graphof FIG. 30, Metglas strips were cut perpendicular to this preferredorientation, and in other experiments represented by other lines on thegraph of FIG. 30, the Metglas ribbons were cut parallel to the preferredorientation. This is represented in FIG. 30 by the words “parallel” and“perpendicular.”

In FIG. 30, two plot or graph lines are also labelled with thedesignation “laminated.” This indicates that strips 200 of Metglashaving a stack configuration similar to what is schematicallyrepresented in FIG. 32 war inserted in the universal coil to capture thedata represented in the corresponding lines on FIG. 30. The two upperlines on FIG. 30 include the designation “side.” As discussed furtherbelow, this “side” designation refers to Metglas strips 202 orientedrelative to a polymer core 204 as shown schematically in FIG. 33.

Comparing the top two lines in FIG. 30, it becomes apparent that whetherthe Metglas strips are cut parallel to or perpendicular to the preferredorientation has someone limited influence or effect on the resultingsignal strength of the magnetic position sensor. This limited effect isalso apparent by similarly comparing the lower two lines (i.e., thelines that each end in a diamond in FIG. 30). Of greater effect, as alsoclearly represented in FIG. 30, is the placement of the Metglas stripsrelative to each other. Lower signal strengths were received from themagnetic position sensor when the two Metglas strips were laminated(i.e., when they had the configuration depicted in schematically in FIG.32).

Looking now more closely at the upper two lines in FIG. 30, which carrythe designation “side,” further details of the experiment are describednext. When one Metglas strip was used it was placed at “position 1”shown in FIG. 33. When two Metglas strips were used, they were placed atposition 1 and position 2, respectively (see FIG. 33). When threeMetglas strips were used, they were placed at positions 1, 2, and 3,shown in FIG. 33. Finally, when four Metglas strips were used in theexperiment, they were placed a positions 1-4 shown in FIG. 33.

FIG. 34 includes, the following six lines:

-   -   1. mV—level: a horizontal line showing the lowest level        (threshold for) voltage which must be met in order for a sensor        to be deemed adequate for one particular system. It is a        reference line on the graph to give meaning to the rest of the        data.    -   2. mV—strip centered: the voltage response of the coil when a        strip of length associated with the X-axis is placed inside the        coil, but centered in the coil such that a little bit of the        strip extends beyond both distal and proximal edges of the coil.    -   3. mm—length offset centered: The same strip as the previous        bullet point, this merely shows the length of the strip (in mm)        that would extend beyond the coil itself. This number has        manufacturability implications.    -   4. mV—strip offset one direction: Voltage response when taking a        strip of length associated with the X-axis, and placing it so        that it is flush on one side of the coil (distal) and only        extends one direction from the coil on the proximal side.    -   5. mm—offset one direction: physical offset when doing the        experiment from the bullet directly above.    -   6. One sided two strips: Until this bullet, all the data is only        with a single strip of Metglas 0.020″ wide. This line is an        estimation of what the voltage response would be if there were        two strips inside the coil instead of one. Also, this Metglas        strip would be assumed to be sticking out only one side like the        two lines labeled “offset one direction.”

Thus, line #1 (referring to the item number above) is a substantiallyhorizontal line near the bottom of the cart representing the lowestlevel of sensor signal strengths that may be used effectively in aparticular system for locating a magnetic position sensor. In otherwords, for some systems, the sensor must produce at least this voltagein order to be recognized by the medical positioning system. Next, thereare two lines on the chart that reference “mm” (i.e., lines #3 and #5 inthe numbered list above). To read the data associated with these twolines, you must use the horizontal scale (“Length of Metglas strip”) andthe right-hand vertical scale (“Metglas offset from coil”). Comparingthese lines, it is apparent that, for the tested configurations, thegreater the offset for a particular length of Metglas, the higher theresulting signal strength. The lower of these two lines carries thedesignation “mm—length of offset centered.” As noted above, this lineshows the length of the strip in millimeters that would extend beyondthe coil itself when the Metglas strip is of the designated length(x-axis). On the other hand, the upper of these two lines (which carriesthe designation “mm—offset one direction”) represents the physicaloffset of the Metglas strip when the distal end of the coil is aligningwith the distal end of the Metglas strip, and the proximal end of theMetglas strip extends proximally from the proximal end of the coil.Comparing the line having the designation “mV—strip centered” to theline carrying the designation “mV—strip offset one direction,” it isapparent that for a given length of Metglas strip, wherein that lengthis longer than the longitudinal length of the coil, if the strip iscentered on the coil and thereby extends the same distance from each endof the coil, the resulting signal strength is greater than if the samelength Metglas strip is mounted relative to the coil so as to extendonly from one end of the coil.

Although several embodiments have been described above with a certaindegree of particularity, those skilled in the art could make numerousalterations to the disclosed embodiments without departing from thespirit of the present disclosure. It is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative only and not limiting. Changes indetail or structure may be made without departing from the presentteachings. The foregoing description and following claims are intendedto cover all such modifications and variations.

Various embodiments are described herein of various apparatuses,systems, and methods. Numerous specific details are set forth to providea thorough understanding of the overall structure, function,manufacture, and use of the embodiments as described in thespecification and illustrated in the accompanying drawings. It will beunderstood by those skilled in the art, however, that the embodimentsmay be practiced without such specific details. In other instances,well-known operations, components, and elements have not been describedin detail so as not to obscure the embodiments described in thespecification. Those of ordinary skill in the art will understand thatthe embodiments described and illustrated herein are non-limitingexamples; and, thus, it can be appreciated that the specific structuraland functional details disclosed herein may be representative and do notnecessarily limit the scope of the embodiments, the scope of which isdefined solely by the appended claims.

Reference throughout the specification to “various embodiments,” “someembodiments,” “one embodiment,” “an embodiment,” or the like, means thata particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment.Thus, appearances of the phrases “in various embodiments,” “in someembodiments,” “in one embodiment,” “in an embodiment,” or the like, inplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,or characteristics may be combined in any suitable manner in one or moreembodiments. Thus, the particular features, structures, orcharacteristics illustrated or described in connection with oneembodiment may be combined, in whole or in part, with the featuresstructures, or characteristics of one or more other embodiments withoutlimitation.

It will be appreciated that the terms “proximal” and “distal” may beused throughout the specification with reference to a clinicianmanipulating one end of an instrument used to treat a patient. The term“proximal” refers to the portion of the instrument closest to theclinician and the term “distal” refers to the portion located furthestfrom the clinician. It will be further appreciated that for concisenessand clarity, spatial terms such as “vertical,” “horizontal,” “up,” and“down” may be used herein with respect to the illustrated embodiments.However, surgical instruments may be used in many orientations andpositions, and these terms are not intended to be limiting and absolute.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialsdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as explicitly set forth hereinsupersedes any conflicting material incorporated herein by reference.Any material, or portion thereof, that is said to be incorporated byreference herein, but which conflicts with existing definitions,statements, or other disclosure material set forth herein will only beincorporated to the extent that no conflict arises between thatincorporated material and the existing disclosure material.

What is claimed is:
 1. A medical device configured for diagnosis ortreatment of a tissue within a body, the medical device comprising thefollowing: an elongate member configured to be received within the body,the elongate member having a lumen extending between a proximal end anda distal end; and a position sensor disposed within the lumen proximatethe distal end of the deformable member, the position sensor comprising:a coil wound to form a central passage and configured to generate acurrent flow when subject to a magnetic field; and a high-permeabilityantenna having at least a portion disposed outside the central passageto concentrate the magnetic field into the coil and increase the currentflow.
 2. The medical device of claim 1, wherein the high-permeabilityantenna comprises a body passing through the central passage and havingan axial length longer than that of the coil.
 3. The medical device ofclaim 2, wherein the body is circumferentially curved in a direction ofwindings of the coil.
 4. The medical device of claim 2, furthercomprising a plurality of bodies disposed adjacent the coil.
 5. Themedical device of claim 1, wherein the high-permeability antennacomprises a first mass disposed adjacent the coil.
 6. The medical deviceof claim 5, wherein the first mass is in contact with the coil outsideof the central passage.
 7. The medical device of claim 5, wherein thefirst mass is spaced axially from the coil.
 8. The medical device ofclaim 5, further comprising a second mass disposed adjacent the coilaxially opposite the first mass.
 9. The medical device of claim 1,wherein the antenna comprises: a mass spaced from the sensor; and aconductor connecting the mass and the coil.
 10. The medical device ofclaim 9, further comprising a shield extending from the mass to surroundthe conductor and the coil
 11. The medical device of claim 10, whereinthe antenna further comprises an opening in the shield adjacent thesensor, or a ground extending through the shield from the sensor. 12.The medical device of claim 1, wherein the antenna comprises metallicglass material.
 13. The medical device of claim 1, further comprising acore disposed completely within the central passage of the coil.
 14. Themedical device of claim 1, wherein the high-permeability antenna has anouter diameter greater than that of the coil.
 15. The medical device ofclaim 1, further comprising: an inner tube extending through the coil;and a conductor extending from the coil toward the proximal end of theelongate, deformable member.
 16. The medical device of claim 1, furthercomprising: an operational element disposed proximal the distal end ofthe elongate, deformable member; and a handle disposed at the proximalend of the elongate, deformable member and adapted to control deflectionof the distal end.
 17. A position sensor assembly for a medical device,the position sensor assembly comprising: a body defining an internallumen; a wire winding supported by the body; and a magnetic flux antennadisposed outside of the wire winding and within the body.
 18. The sensorassembly of claim 17, wherein the antenna comprises a thin strip ofmaterial.
 19. The sensor assembly of claim 17, wherein the antennacomprises a mass of material having a permeability greater than that ofthe wire winding.
 20. The sensor assembly of claim 17, furthercomprising a core disposed within the wire winding.
 21. The sensorassembly of claim 17, further comprising a plurality of magnetic fluxantennas disposed outside of the wire winding and within the body. 22.The sensor assembly of claim 17, further comprising: a conductorelectrically coupling the wire winding and the magnetic flux antenna;and a shield surrounding the wire winding and the conductor.
 23. Amedical device comprising: an elongate sheath defining a lumen; aposition sensor disposed within the lumen; an electrode exposed to anexterior of the elongate sheath; and a magnetic antenna disposed withinthe sheath apart from the position sensor.
 24. The medical device ofclaim 23, wherein the position sensor comprises a coil.
 25. The medicaldevice of claim 24, wherein the coil includes a core having apermeability greater than that of air.
 26. The medical device of claim25, wherein the permeability of the magnetic antenna is greater thanthat of the core.
 27. The medical device of claim 24, wherein themagnetic antenna comprises a thin strip of material extending generallyparallel to a central axis of the coil.
 28. The medical device of claim24, further comprising an additional magnetic antenna disposed apartfrom the other magnetic antenna.
 29. A method of increasing the signaloutput of a magnetic position sensor, the method comprising: configuringa magnetic position sensor comprising a coil to generate a current flowwhen subject to a magnetic field; mounting the position sensor within amedical device; and placing at least a portion of a high permeabilityantenna outside of the magnetic position sensor so as to be configuredto concentrate a magnetic field into the coil and increase the currentflow.
 30. The method of claim 29, wherein the high permeability antennais positioned to funnel magnetic flux to the magnetic position sensor.31. The method of claim 29, further comprising spacing the highpermeability antenna from the magnetic position sensor.
 32. The methodof claim 29, further comprising shaping the high permeability antenna tobe long and skinny.
 33. The method of claim 29, further comprisingconnecting the magnetic position sensor and the high permeabilityantenna with a conductor.
 34. The method of claim 33, further comprisingshielding the magnetic position sensor and the conductor with a highpermeability structure.